1. Field of the Invention
The invention generally relates to a sensing circuit, and more particularly, to a current sensing circuit.
2. Description of Related Art
In order to save the consumed power of a display or provide better image quality of a display, an ambient-light sensor is broadly used in electronic apparatuses such as mobile phone, handheld apparatus and image display. Nearly all of ambient-light sensors take a photodiode architecture, which requires a voltage power for operation. A photo sensor produces different currents according to different sensed light intensities, so that a digital reading result is provided by means of a current sensing circuit inside the photo sensor.
The applicable sensing range of an ambient-light sensor is quite large, from several Lux to tens of thousands Lux. Generally, the current sensing circuit of an ambient-light sensor requires an analog-to-digital converter (ADC) with over 16-bits to meet the function need. In practical applications however, although the sensing range of an ambient-light sensor is very broad, but the precision required by the current sensing circuit is somehow different responding to the sensed light source intensity. For example, when a light source is darker (below 1000 Lux), the precision required by an ambient-light sensor is about 1 Lux and the corresponding precision of the current sensing circuit is relatively high; when a light source is lighter (over 10000 Lux), the precision required by an ambient-light sensor is about 20-30 Lux and the corresponding precision of the current sensing circuit is relatively lower.
Hence, it is necessary for the related manufactures to provide a current sensing circuit with different precisions responding to different current sensing ranges.